Thin film stacks

ABSTRACT

A thin film stack can include a metal substrate having a thickness of from 200 angstroms to 5000 angstroms and a passivation barrier disposed on the metal substrate at a thickness of from 600 angstroms to 1650 angstroms. The passivation barrier can include a dielectric layer and an atomic layer deposition (ALD) layer disposed on the dielectric layer. The dielectric layer can have a thickness of from 550 to 950 angstroms. The ALD layer can have a thickness from 50 to 700 angstroms.

BACKGROUND

In a typical inkjet printing system, an inkjet printhead ejects fluid(e.g., ink) droplets through a plurality of nozzles toward a printmedium, such as a paper or other substrate, to print an image onto theprint medium. The nozzles are generally arranged in one or more arraysor patterns, such that properly sequenced ejection of ink from thenozzles causes characters or other images to be printed on the printmedium as the printhead and the print medium are moved relative to oneanother.

Because the ejection process is repeated thousands of times per secondduring printing, collapsing vapor bubbles can contribute to an adverseeffect of damaging a heating element used in the printing process. Therepeated collapsing of the vapor bubbles leads to cavitation damage atthe surface material that coats the heating element. Each of thesecollapse events can thus contribute to ablation of the coating material.Once ink penetrates the surface material coating, the heating elementand contacts the hot, high voltage resistor surface and rapid corrosionand physical destruction of the resistor soon follows, rendering theheating element ineffective. There are also other examples of systems,outside of the inkjet arts, where structures may undergo contact withharsh environments. As such, research and development continues in thearea of protective films used in various applications that can provideimproved performance.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the present disclosure will beapparent from the detailed description which follows, taken inconjunction with the accompanying drawings, which together illustrate,by way of example, features of the present technology.

FIG. 1 is an example cross-section schematic view of a thin film stackin accordance with the present disclosure;

FIG. 2 is an example cross-sectional schematic view of a portion of athermal inkjet printhead stack in accordance with the presentdisclosure; and

FIG. 3 is an example graph comparing power requirements for various inkdrop volumes in two example thermal inkjet printheads.

Reference will now be made to specific examples illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of thepresent disclosure is thereby intended.

DETAILED DESCRIPTION

In thermal inkjet (TIJ) technology, the passivation layer of a TIJprinthead can be directly related to energy efficiency, functionality,reliability, and other properties of the printhead. Often thepassivation layer can be deposited by plasma-enhanced chemical vapordeposition (PECVD). While PECVD can be a powerful deposition technique,it can also result in a number of defects and step coverage limitationsthat can render the film to be relatively thick in order to maintainchemical robustness. However, thicker passivation layers can cause theTIJ printhead to be less energy efficient.

The present disclosure is drawn to thin film stacks, methods ofmanufacturing thin film stacks, and thermal inkjet (TIJ) printheadstacks that can help overcome some of the challenges described above. Itis noted that when discussing a thin film stack, a method ofmanufacturing a thin film stack, or a TIJ printhead stack, each of thesediscussions can be considered applicable to each of these examples,whether or not they are explicitly discussed in the context of thatspecific example. Thus, for example, in discussing a dielectric layerfor a passivation barrier in the thin film stack, such a dielectriclayer can also be used in a method of manufacturing a thin film stack orin a TIJ printhead stack, and vice versa.

As such, with the present discussion in mind, a thin film stack caninclude a metal substrate having a thickness of from 200 angstroms to20,000 angstroms. A passivation barrier can be disposed on the metalsubstrate at a thickness of from 600 angstroms to 1650 angstroms. Thepassivation barrier can include a dielectric layer and an atomic layerdeposition (ALD) layer disposed on the dielectric layer. The dielectriclayer can have a thickness from 550 to 950 angstroms. The ALD layer canhave a thickness from 50 to 700 angstroms.

One example of a thin film stack is illustrated in FIG. 1. The thin filmstack 100 can include a metal substrate 105. A dielectric layer 110 canbe disposed on the metal substrate. An ALD layer can be disposed on thedielectric layer. The combined dielectric layer and ALD layer can form apassivation barrier on the metal substrate.

The metal substrate can be any suitable metal substrate. In someexamples, the metal substrate can be made of a resistor material. Inother specific examples, the substrate can include TaAl, WSiN, TaSiN,TaN, Ta₂O₅, the like, or a combination thereof.

In further detail, the metal substrate can have a thickness of from 200angstroms to 20,000 angstrom, or the metal substrate can have athickness of from 200 angstroms to 5000 angstroms. In another example,the metal substrate can have a thickness of from 200 angstroms to 3000angstroms.

The passivation barrier can generally include two layers or layer types.While the two layers can be formed at different thicknesses relative toone another, the overall passivation barrier can typically have athickness of from 600 angstroms to 1650 angstroms. In some additionalexamples, the passivation barrier can have a thickness of from 700angstroms to 1000 or 1400 angstroms.

One of the layers of the passivation barrier can include a dielectriclayer, which can be disposed on the metal substrate. In some examples,the dielectric layer can have a thickness of from 550 angstroms to 950angstroms. In other examples, the dielectric layer can have a thicknessof from 600 angstroms to 800 angstroms.

The dielectric layer can be of any suitable dielectric material.Non-limiting examples can include SiO₂, SiN, SiO_(x)N_(y), Al₂O₃, ZrO₂,undoped silicate glass, the like, or a combination thereof. In onespecific example, the dielectric layer can include SiN.

The ALD layer can be disposed on the dielectric layer. Generally, theALD layer can have a thickness of from 50 angstroms to 700 angstroms. Insome examples, the ALD layer can have a thickness of from 50 angstromsto 200 angstroms or 450 angstroms.

In further detail, in some examples, the ALD layer can be pinhole free.Whether the ALD layer is pinhole free can depend on the material orcombination of materials forming the ALD layer. A pinhole freelayer canbe verified by a number of methods. One such method can include forminga silicon nitride layer, or other suitable dielectric layer, andapplying an ALD layer with a suitable pinhole free material, such asHfO₂, for example, to cover the silicon nitride layer. A buffered oxideetch (BOE) solution can then be disposed on the ALD layer covering thesilicon nitride layer. If the BOE solution etches the lower siliconnitride layer, the BOE solution was able to penetrate the ALD layer,indicating that the ALD layer is not pinhole free. If the BOE solutiondoes not etch the lower silicon nitride layer, the BOE was not able topenetrate the ALD layer, which can indicate that the ALD layer ispinhole free.

The ALD layer can include a number of suitable materials. Non-limitingexamples can include HfO₂, ZrO₂, HfSi_(x)O_(y), WSi_(x)O_(y), Al₂O₃,Ta₂O₅, SiN, the like, or a combination thereof. In one specific example,the ALD layer can include HfO₂. In another example, the ALD layer caninclude SiN. In another example, the ALD layer can be a metal oxidelayer.

Turning now to a method of manufacturing a thin film stack, the methodcan include preparing a metal substrate having a thickness of from 200angstroms to 20,000 angstroms. A passivation barrier can be deposited onthe metal substrate at a thickness of from 600 angstroms to 1650angstroms. Depositing the passivation barrier can include depositing adielectric layer on the metal substrate at a thickness of 550 angstromsto 950 angstroms and depositing an ALD layer on the dielectric layer ata thickness of 50 angstroms to 700 angstroms.

The metal substrate can be prepared using any suitable depositiontechnique. Non-limiting examples can include chemical vapor deposition(CVD), physical vapor deposition (PVD), epitaxy, electrodeposition,sputtering, the like, or combinations thereof. Typically, the metalsubstrate can have a composition and thickness as described above.

With respect to the passivation barrier disposed on the metal substrate,this barrier can also have a composition and thickness as describedabove. Typically, the thickness of the passivation barrier does notexceed 1650 angstroms. Such thin passivation barriers can allow thedevice into which they are incorporated to be more energy efficient thanan equivalent device incorporating a thicker passivation barrier, suchas a 2000 to 3000 angstrom passivation barrier.

However, it can be challenging to prepare thin passivation barriersbecause of pinhole defects and step coverage limitations associated withsome deposition methods. Thus, while the dielectric layer of the presentpassivation barrier can be deposited using any suitable depositionmethod, such as PECVD for example, the layer disposed on the dielectriclayer can typically be deposited using atomic layer deposition or ALD.Atomic layer deposition can provide very thin layers that can, in somecases, be pinhole free, as described above. Because of the chemicalrobustness of the ALD layer, the dielectric layer can also be very thin.Thus, the thin ALD layer can typically allow the overall passivationbarrier to be thin and energy efficient. Further still, the chemicalrobustness of the ALD layer can also decrease or eliminate the need fora protective layer to be disposed on the passivation barrier, making theoverall thin film stack thinner still. As such, this passivation barriercan be desirable for a number of device applications.

In one specific example, the passivation barrier can be included in athermal inkjet printhead stack. The thermal inkjet (TIJ) printhead stackcan include an insulated substrate and a resistor disposed on theinsulated substrate at a thickness of from 200 angstroms to 20,000angstroms. A resistor passivation barrier can be disposed on theresistor at a thickness of from 600 angstroms to 1650 angstroms. Theresistor passivation barrier can include a dielectric layer disposed onthe resistor at a thickness of from 550 angstroms to 950 angstroms. Theresistor passivation barrier can also include an ALD layer disposed onthe dielectric layer at a thickness of from 50 angstroms to 700angstroms. In some examples, the TIJ printhead stack does not include aprotective layer disposed on the resistor passivation layer. In someexamples, the thermal inkjet printhead stack can also include a pair ofconductors electrically coupled to the resistor. A conductor passivationlayer can also be disposed on the pair of conductors. In some examples,the conductor passivation layer can be the same as resistor passivationbarrier.

An example thermal inkjet printhead stack is illustrated in FIG. 2 at200. Specifically, a silicon wafer 210 is shown having an electricalinsulating layer 220 applied thereto. To the insulating layer can beapplied a resistor 230, which can be prepared using any known resistormaterial known in the thermal inkjet printing arts, such as TaAl, WSiN,TaSiN, TaN, or Ta₂O₅. A suitable average thickness for the resistor canbe from 0.02 microns to 0.5 microns or from 0.02 microns to 2 microns,though thicknesses outside of this range can also be used. Furthermore,the resistor, as described, can be doped with any material suitable forachieving desired electrical properties, including, but not limited to,resistivity. In some examples, the resistor can have a bulk electricalresistivity of from 200 μΩ·cm to 200 μΩ·cm, 200 μΩ·cm to 10,000 μΩ·cm,or from 200 μΩ·cm to 2000 μΩ·cm.

The resistor 230 can likewise be in electrical communication with a pairof conductors 240 positioned on either side of the resistor. Theseconductors can act as electrodes for the resistor. In this example, theconductors are also disposed on the insulating layer 220, though thisarrangement is merely exemplary. The conductors can be of any materialsuitable for use as conductors, such as gold, aluminum, copper, thelike, or an alloy thereof, such as an alloy of aluminum and copper, forexample.

Furthermore, conductor passivation layers 250, which can also beinsulating, can be disposed on the conductors to prevent contact betweenthe ink 260 and the conductors 240. A suitable average thickness for theconductors can be from 0.1 micron to 2 microns, and a suitable averagethickness for the conductor passivation layers can be from 0.02 micronto 1 micron, though thicknesses outside of this range can also besuitable. However, where the conductor passivation layer is the same asthe resistor passivation barrier, the conductor passivation layer canhave the same thicknesses described for the resistor passivationbarrier.

Insulating materials that can be used for the electrical insulatinglayer 220, the conductor passivation layers 250, or any other insulatinglayer can be SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, HfSi_(x)O_(y), WSi_(x)O_(y),or undoped silicate glass, for example. The electrical insulating filmsor conductor passivation layers, for example, can be formed by thermaloxidation of the conductors or deposition of an electrically insulatingthin film.

To the resistor 230, a resistor passivation barrier 270 can likewise beapplied. As previously described, the resistor passivation barrier caninclude a dielectric layer 271 and an ALD layer 272 disposed on thedielectric layer. These layers can be prepared as described above. Also,it is noted that the resistor passivation barrier and the conductorpassivation layers 250 can be integrated as a single layer, or mayremain as separate, adjacent layers. Because the resistor passivationbarrier is sufficiently chemically robust alone, the TIJ printhead stackcan exclude a protective layer, which can typically be disposed on thepassivation layer. It is also noted that many other types or positioningof layers can also be used as would be appreciated by one skilled in theart after considering the present disclosure.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise.

As used herein, “devoid of” refers to the absence of materials inquantities other than trace amounts, such as impurities.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 5 at % to about 90 at %”should be interpreted to include not only the explicitly recited valuesof about 5 at % to about 90 at %, but also include individual values andsub-ranges within the indicated range. Thus, included in this numericalrange are individual values such as 6, 7.5, and 8 and sub-ranges such asfrom 5-75, from 7-80, and from 9-85, etc. This same principle applies toranges reciting only one numerical value. Furthermore, such aninterpretation should apply regardless of the breadth of the range orthe characteristics being described.

The following example illustrates features of the disclosure that arepresently known. Thus, this example should not be considered as alimitation of the present technology, but is merely in place to teachhow to make compositions of the present disclosure. As such, arepresentative number of compositions and their methods of manufactureare disclosed herein.

Example Turn on Energy Test for Passivation Barrier

Various thermal inkjet (TIJ) printhead stacks were prepared havingidentical structural configurations except that the passivation barrierwas different for each of the printhead stacks. Specifically, Sample 1(control sample) included a SiN layer coated with a SiC layer. Bothlayers were deposited using PECVD. In contrast, Samples 2-9 included aSiN dielectric layer coated with a HfO₂ layer. The SiN layer wasdeposited using PECVD and the HfO₂ layer was deposited using ALD. Thethicknesses in angstroms for each of the layers included in the variouspassivation barriers are described more fully in Table 1. None of theprinthead stacks included a cavitation layer deposited on thepassivation barrier.

The total thickness of the passivation barrier for Sample 1 was about2500 angstroms, which is not uncommon for passivation barriers inthermal inkjet printhead stacks. In contrast, Samples 2-9 had totalthicknesses ranging from 700 to 1000 angstroms, less than half thethickness of the control sample.

TABLE 1 Sample SiN SiC HfO₂ Total 1 1670 830 n/a 2500 2 600 n/a 100 7003 600 n/a 200 800 4 700 n/a 50 750 5 700 n/a 100 800 6 700 n/a 200 900 7800 n/a 50 850 8 800 n/a 100 900 9 800 n/a 200 1000

Energy to each of the TIJ printhead stacks was ramped down until theprinthead stopped printing at a steady drop weight. This drop off pointwas compared between the control sample (Sample 1) and each of the testsamples (Samples 2-9). This is a measurement of the pulse durationrequired to fire a particular drop size. The longer the pulse durationrequired to print a particular drop weight, the greater the energyconsumption. Table 2 illustrates the percent decrease in energyconsumption for Samples 2-9 as compared to Sample 1.

TABLE 2 Sample % Decrease In Energy Consumption 2 30% 3 27% 4 30% 5 31%6 25% 7 30% 8 25% 9 25%

As depicted in Table 2, each of Samples 2-9 exhibited at least a 25%decrease in energy consumption to achieve a predetermined drop volume ascompared to Sample 1. Further, some of the samples exhibited a 30%decrease in energy consumption, or more, as compared to Sample 1.

FIG. 3 provides a comparative graphical illustration of the energyrequirements to eject various drop volumes from Sample 1 as compared toSample 7. The energy requirements for each drop volume was determined asdescribed above. It is noted that Samples 2-9 all exhibited fairlysimilar turn on energy profiles to Sample 7. As such, only Sample 7 isillustrated for the sake of clarity. As can be seen in FIG. 3, Sample 7did not require as many microjoules of energy as Sample 1 to ejectequivalent drop volumes of ink. In fact, Sample 7 required less energyto eject a 10 ng ink droplet than Sample 1 required to eject a 2 ng inkdroplet.

While the present technology has been described with reference tocertain examples, those skilled in the art will appreciate that variousmodifications, changes, omissions, and substitutions can be made withoutdeparting from the spirit of the present technology. It is intended,therefore, that the present technology be limited only by the scope ofthe following claims.

What is claimed is:
 1. A thin film stack, comprising: a metal substratehaving a thickness of from 200 angstroms to 20,000 angstroms; and apassivation barrier disposed on the metal substrate at a thickness offrom 600 angstroms to 1650 angstroms, the passivation barrier,comprising: a dielectric layer having a thickness of from 550 to 950angstroms, and an ALD layer disposed on the dielectric layer, the metaloxide layer having a thickness of from 50 to 700 angstroms.
 2. The thinfilm stack of claim 1, wherein the ALD layer is pinhole free.
 3. Thethin film stack of claim 1, wherein the metal substrate comprises TaAl,WSiN, TaSiN, TaN, Ta₂O₅, or a combination thereof.
 4. The thin filmstack of claim 1, wherein the passivation barrier has a thickness from700 angstroms to 1400 angstroms.
 5. The thin film stack of claim 1,wherein the dielectric layer has a thickness of from 600 to 800angstroms, and the ALD layer has a thickness from 50 angstroms to 450angstroms.
 6. The thin film stack of claim 1, wherein the dielectriclayer comprises SiO₂, SiN, SiO_(x)N_(y), Al₂O₃, ZrO₂, undoped silicateglass, or a combination thereof.
 7. The thin film stack of claim 1,wherein the ALD layer comprises HfO₂, ZrO₂, HfSi_(x)O_(y), WSi_(x)O_(y),Al₂O₃, Ta₂O₅, SiN, or a combination thereof.
 8. A method ofmanufacturing a thin film stack, comprising: preparing a metal substratehaving a thickness of from 200 to 5000 angstroms; and depositing apassivation barrier on the metal substrate at a thickness of from 600angstroms to 1400 angstroms, wherein depositing the passivation barriercomprises: depositing a dielectric layer on the metal substrate at athickness of 550 to 950 angstroms, and depositing an ALD layer on thedielectric layer at a thickness of 50 to 700 angstroms.
 9. The method ofclaim 8, wherein depositing the dielectric layer is performed byplasma-enhanced chemical vapor deposition (PECVD).
 10. The method ofclaim 8, wherein the ALD layer has a thickness of 50 to 450 angstroms.11. A thermal inkjet printhead stack, comprising: an insulatedsubstrate; a resistor disposed on the insulated substrate at a thicknessof from 200 angstroms to 5000 angstroms; and a resistor passivationbarrier disposed on the resistor at a thickness of from 600 angstroms to1400 angstroms, said resistor passivation barrier, comprising: adielectric layer disposed on the resistor at a thickness of from 550angstroms to 950 angstroms, and an ALD layer disposed on the dielectriclayer at a thickness of from 50 angstroms to 700 angstroms, wherein thethermal inkjet printhead stack does not include a protective layerdisposed on the resistor passivation layer.
 12. The thermal inkjetprinthead stack of claim 11, wherein the resistor has a bulk electricalresistivity of from 200 μΩ·cm to 200 Ω·cm.
 13. The thermal inkjetprinthead stack of claim 11, further comprising a pair of conductorselectrically coupled to the resistor.
 14. The thermal inkjet printheadstack of claim 13, wherein the resistor passivation barrier is alsodisposed on the pair of conductors.
 15. The thermal inkjet printheadstack of claim 11, wherein the ALD layer is pinhole free.